1. Field of the Invention
This invention relates to the serious dangers that are associated with the release of hazardous airborne contaminants into the environment. More specifically, this invention is intended to protect the environment from fugitive asbestos fibers that are released during transportation and unloading of such material, and to protect workers who must unload vehicles used to transport and dispose asbestos from EPA Demo/Remo and other source sites.
2. Description of the Prior Art
Asbestos fibers fall into the generic classification of hazardous particulates and are a well known carcinogenic hazard to humans and animals. Typical environmental standards refer to fibers that are 5 microns or greater in length with an aspect ratio of 3 to 1 or greater. The testing standards presently in use utilize a phase contrast optical microscope with about 440.times. magnification. These testing methods are not capable of seeing fibers below about 0.3 microns in diameter.
Actually, the average asbestos fiber is about 0.1 microns in diameter. Therefore, using the present standards and equipment, for every fiber counted there is present as many as 30 fibers uncounted. This is coupled with the standard that fibers shorter than 5 microns in length are not considered. It is now accepted that the thinner fibers are the most dangerous threat to human health. While present standards indicate "satisfactory condition" with concentrations less than 2.0 fibers per cubic centimeter, this, in reality, means that the standards allow an actual concentration of about 60 fibers per cubic centimeter, if the thinner fibers were counted. The asbestos fibers, in particular those that are thinner and shorter, remain airborne for considerable lengths of time and contaminate large volumes of air to form a substantial hazard to the environment and to the persons working or living in the area. The asbestos containing materials (ACM) are presently being handled in accordance with current EPA and DOT regulations; bagged and sometimes containerized, in theoretically "leak tight" containers. Depending upon such factors as temperature, humidity, storage, dehydration and trip duration, the ACMs, although bagged and containerized, are tossed, dropped, jostled, and punctured and the compression from the weight of the bags and containers forces asbestos fibers to escape into the trailer and into the outside air during transportation and disposal.
Many asbestos removal projects involve placing the ACMs in a six mil polyvinyl bag, then placing the bagged ACMs in another six mil polyvinyl bag. However, this arrangement is not leak tight to the smallest fibers due to conventional closure methods (twisting and taping of open ends of poly vinyl bags) and the possibility that micropores in the bag material result in the bag material not providing sufficient fiber containment during the bagging process. The bags are further jostled, punctured, and compressed during transit as the load settles and the bagged materials are compressed under their own weight. The outside environment is ultimately subjected to a substantial risk due to the high asbestos concentration buildup that occurs within the trailer. This buildup tends to be released to atmosphere when the trailer is opened at the final disposal site. Due to the lightness of the released fibers, especially the smallest fibers, asbestos may be carried far from the disposal site, where it could settle and be inhaled or ingested by humans.
U.S. Pat. No. 4,979,967 to Walker discloses one known transport system for hauling airborne contaminants such as asbestos. This system includes a fan for inducing an underpressure in a trailer, with a HEPA filter positioned between the trailer interior and the fan to filter out contaminants before they can be passed to atmosphere. This "negative pressure" system can be viewed as an adaptation of the negative pressure clean room concept that was first disclosed in U.S. Pat. No. 4,604,111 to Natale. The Walker system further includes sprayers for wetting the contaminants in order to keep dust down. Despite the wetting and filtration precautions, a significant release of fugitive fibers may be expected with this type of system at a disposal site.
It is clear there exists a long and unfilled need in the prior art for a transport system for hazardous airborne contaminants that reduces or eliminates escape of hazardous airborne contaminants to the atmosphere, both during transportation and unloading at a disposal site.